Electronic instruments answering the general definition mentioned hereinbefore are already known. EP Patent Application No. 1 109 084 A1 and EP Patent Application 1 134 630 A1 for example disclose such electronic instruments. EP Patent Application No. 1 109 084 A1 discloses in particular such a solution wherein at least one control member of the aforementioned type is exploited to recharge an electric accumulator housed in the instrument whereas EP Patent Application No. 1 134 630 A1 discloses a solution wherein at least one control member is exploited to transmit and/or receive data from the electronic instrument.
The advantage of these prior art solutions (which also goes for the present invention) lies in the use of one or more control members (conventionally of the push-button type) for electrically connecting the electronic instrument to an external unit, for example a personal computer. Consequently, no specific contact element is necessary to establish an electrical connection between the electronic instrument and the external unit, this electrical connection being established as soon as the control member or members configured to have the aforementioned dual function are brought into the pushed-in position.
One peculiarity of the two aforementioned prior solutions lies in the use of the retaining element of the control member (similar to a retaining key) as the contact element for fulfilling the conventional function of the control member, namely controlling the functions of the electronic instrument. Another peculiarity of these prior solutions lies in the fact that the stem of the control member, in the non-pushed in position, is floating from the electrical point of view. In the non-pushed in position, electric charges are thus able to accumulate on the stem of the control member. When the control member is actuated, this accumulation of electric charges can then be carried across the terminals with which the control member is brought into contact and cause damage, in particular to the electronic circuit of the instrument. This constitutes a critical problem for solutions of the aforementioned type, given that the control member fulfils two functions and it establishes a direct connection with sensitive components of the electronic circuit of the instrument, in particular its processor unit and the associated memories.
One solution to overcome this problem can consist in protecting the terminals with which the control member is brought into contact by means of electric protective components allowing a path to be established for discharging the accumulated electric charges. These are well known protective components, called ESD (“electro-static-discharge”) components. It is, however, desirable to find a solution that ensures that the electric charges cannot accumulate in the first place on the stem of the control member when the latter is in the non-pushed in position.